During certain operations such as cardiopulmonary bypass operations, the function of the heart and lungs are interrupted and blood is artificially handled. The patient's body temperature is lowered and the heart itself stops beating. Circulation is maintained by withdrawal of the venous return stream through a venous cannula inserted into the right atrium, passed to a venous reservoir, passed through a blood pump (artificial heart) to a blood oxygenator (artificial lung), arterial blood filter which removes fine air bubbles and any undesirable particles that may be present in the blood before it is returned to the patient through an aortic annula.
Also, during a cardiopulmonary bypass operation, it is essential to suction away the various fluids including, for example, air, debris such as bone chips, blood, saline solution, liquids applied to the heart and the like. This must be accomplished as quickly and efficiently as possible without causing injury to the patient primarily in order to avoid damage to the heart from the fluid pressure but also to aid the surgeon.
Such fluids are termed "cardiotomy blood" which requires filtration prior to reinfusion. This term is distinguished from "shed blood" used to describe the blood accumulation which takes place after surgery and which is characterized by being of much higher quality and requiring less filtration.
Normally, a cardiotomy reservoir is used in conjunction with relatively high vacuum suction in order to remove and collect the cardiotomy blood and other liquids as quickly as possible. This vacuum can be provided through a standard air driven cardiotomy sucker through a roller pump. Use of the roller pump is clearly the method of choice since the suction can be carefully controlled and monitored.
Blood collected within a cardiotomy reservoir can be filtered and defoamed to remove air, debris and clots after which it can be reinfused to the patient. This can take place during or after surgery.
In recent years it has been found desirable during surgery to combine the cardiotomy blood with the venous blood in a single reservoir which replaces the separate cardiotomy reservoir and separate venous reservoir formerly used. This created some problems since the flow rate of venous blood is about 3 times greater than the flow of cardiotomy blood. Moreover, the venous blood is clean requiring only minimal defoaming and filtration. When venous blood was subjected to the same filtration as used for cardiotomy blood, it was found detrimental to the blood cells.
In recent years, in order to overcome this problem, separate filter chambers were provided within a single chamber to provide for separate filtering of venous blood and cardiotomy blood. Such a device is described in U.S. Pat. No. 4,642,089. This device comprises a hollow housing made of a rigid material having disposed substantially annularly a filter chamber spaced from the exterior walls of the unit. The filter chamber contains two separate chambers, an upper chamber for introduction and filtration of cardiotomy blood through a non-woven depth filter and a defoaming material and a lower chamber including a defoaming filter material but free of the non-woven depth filter.
Cardiotomy blood enters the upper filter chamber from the top of the unit and venous blood enters the lower filter chamber through the bottom of the unit. Blood entering either chamber passes through the filter and/or defoamer and is combined in a space defined by the outer walls and the filter chamber where it can be withdrawn for reinfusion to the patient.
There are several drawbacks associated with the cardiotomy/venous blood unit of U.S. Pat. No. 4,642,089. For example, venous blood, which is normally obtained by gravity flow, enters the unit from the bottom of the unit into the bottom venous chamber, where it passes through the defoaming filter prior to discharge through a bottom discharge port. The disadvantage is that this condition can lead to resistance to entry of venous blood and to discharge in the bottom leading to stasis. When the bottom or venous compartment is partially filled, the incoming venous blood must enter against this resistance. There is an inverted flow director facing downwardly within the venous chamber for direction of blood from the venous inlet toward the filter. However, this flow director is insufficient to avoid stasis. It is not good to have blood standing anywhere in the reservoir due to the formation of clots.
In U.S. Pat. No. 4,642,089, the upper cardiotomy chamber has a baffle spaced from the inlet to the cardiotomy chamber for purposes of directing the cardiotomy blood flow downwardly into the cardiotomy chamber. A flow director in the form of a truncated cone having 4 opposed fins extends the length of the cardiotomy chamber to prevent splashing and to direct the cardiotomy blood flow against the surrounding filter. The filter is comprised of a non-woven depth filter material which filters by excluding a range of size of particles and is thus only partially effective for filtration. Finally, this device does not permit postoperative drainage of shed blood or pleural drainage.
After surgery, it is desirable to provide drainage of shed blood and fluid from the area around the operative site using relatively low suction pressure as compared with the suction used for cardiotomy suction. This is a requirement to avoid injury to body tissues.
Similar low suction pressure requirements exist for pleural drainage whereby fluid, blood and gases including air are removed from the pleural space between the lungs and the rib cage to maintain the lung in the fully expanded condition. The need for pleural drainage can arise as a result of surgery, piercing of the rib cage or from illness.
In addition to low suction pressure, it is a second requirement to prevent backflow of air to the patient which could cause an emboli or introduce microorganisms into the shed blood or pleural drainage fluids to the detriment of the patient. This can happen if the vacuum is interrupted such as during transfer of the patient.
In the past such postoperative or pleural drainage has been effected by means of a three bottle system. This system consisted of a collection bottle, a liquid seal for gases to bubble through and prevent backflow into the patient, and vacuum regulation of suction flow.
It is desirable for the above reasons to closely monitor negative or vacuum pressures during pleural drainage. Also, if the vacuum is lost for any reason, a water seal prevents air from flowing freely back into the pleural cavity. When the patient coughs, the negative pressure can be excessive which can result in water being sucked out of the manometer into the water seal or collection chamber.
More recently, the three bottle system has been combined with a flexible and detachable blood bag in a device of the type described in U.S. Pat. No. 4,781,707. This device collected shed blood in a detachable blood bag for reinfusion to the patient. This device, however, is not suitable for cardiotomy and venous blood collection during surgery.